Treatment of diabetic complications with certain spiro-imidazolidine-diones

ABSTRACT

Inhibition of aldose reductase activity with tetracyclic spiro-hydantoins, new tetracyclic spirohydantoin derivatives useful in the treatment of complications arising from diabetes mellitus, and a process for preparing spiro-imidazolidine-diones by reacting a mono- or di-fluorofluorene with an excess of oxygen and a tetralkyl- or arylalkyl-trialkyl-ammonium hydroxide are disclosed.

This is a continuation-in-part application of application Ser. No. 368,630 filed Apr. 15, 1982, now U.S. Pat. No. 4,436,745; application Ser. No. 368,631 filed Apr. 15, 1982, now U.S. Pat. No. 4,438,272; and application Ser. No. 368,632, filed Apr. 15, 1982, now abandoned.

This invention relates to the method of inhibiting aldose reductase activity with hydantoin derivatives and new and useful hydantoin derivatives in medicinal chemistry. This invention particularly concerns the use of spiro-hydantoin compounds with a substituted and unsubstituted fluorene ring in the treatment of complications arising from diabetes mellitus such as cataracts and neuropathy.

Further, this invention relates to a process for the manufacture of spiro-(fluorofluoren-9,4'-imidazolidine)-2',5'-diones and spiro-(difluorofluoren-9,4'-imidazolidine)-2',5'-diones. The process invention relates to the general preparation of spiro-(fluoren-9,4'-imidazolidine)-2',5'-diones that are substituted in position 1, 2, 3, or 4 with a fluoro group and/or spiro-(difluorofluoren-9-4'-imidazolidine)-2',5'-diones which are substitued in a combination of the 1, 2, 3, or 4 positions and in the 5, 6, 7, or 8 positions with a fluoro group. More particularly, the invention is concerned with the preparation of dl-spiro-(2-fluorofluoren-9,4'-imidazolidine)-2',5'-dione and spiro-(2,7-difluorofluoren-9,4'-imidazolidine)-2,5-dione.

In diabetes mellitus certain tissues are subject to exposure to high glucose levels. In the lens of the eye, nerves, kidney, retina and other tissues is the enzyme aldose reductase. The latter is mainly responsible for the reduction of aldoses such as glucose to a polyol such as sorbitol and galactose to galactitol at the expense of NADPH. Accumulations of polyols such as sorbitol in diabetic subjects cause and/or are associated with diabetic complications including those of a lenticular, reninal, neuronal and renal nature. These complications are generally known as diabetic cataract, retinopathy, neuropathy, and nephropathy respectively. Elevated polyol such as sorbitol or galactitol in the eye lens lead to cataract and loss of lens transparency. Elevated polyol such as sorbitol in the peripheral nerves interferes with normal nervous function. Aldose reductase action on elevated glucose and/or galactose is also implicated in causing vasculature basement membrane thickening per se in the retinal capillaries and certain kidney tissues. Aldose reductase inhibitors inhibit the activity of aldose reductase. Hence, aldose reductase inhibitors prevent the production of polyols which directly or indirectly lead to the formation of cataracts, reduced nerve conduction/function, and some diabetic vasculature pathophysiology.

K. Sestanj et al. in the U.S. Pat. No. 3,821,383 describes 1,3-dioxo-1H-benz-[d,3]-isoquinoline-2(3H)-acetic acid and derivatives thereof as aldose reductase inhibitors. Further, the search for effective antidiabetic agents to prevent or arrest chronic complications such as cataracts, neuropathy and retinopathy has revealed that particular spiro-hydantoin compounds are useful as aldose reductase inhibitors.

Sarges, U.S. Pat. No. 4,117,230 describes a series of spiro-hydantoin compounds which include the 6-fluoro and 6,8-dichloro derivatives of spiro-chroman-imidazolidinediones.

Sarges, U.S. Pat. No. 4,130,714 describes enhanced activity of specific dextrotatory spiro-hydantoin compounds such as

d-spiro-[6-fluoro-chroman-4,4'-imidazolidine]-2',5'-dione and

d-spiro-[6'-fluoro-imidazolidine-4,4'-thiochroman]-2,5'dione in preventing chronic selected diabetic complications.

Sarges et al., U.S. Pat. Nos. 4,181,728 and 4,181,729 describe spiro-polycyclicimidazolidinedione derivatives and phenyl or phenoxy substituted spiro-imidazolidinedione derivatives, respectively, which are useful to inhibit the enzymatic reduction of aldoses to prevent or reduce harmful and unwanted accumulations of polyols in the lens and nerves.

Methylthio and methylsulfinyl (also called methylsulfoxyl) substituted spiro-chromanimidazolidinediones which are the subject of a contemporaneously filed application also are useful as aldose reductase inhibitors. With respect to sulphur containing derivatives in the instant invention, a methylsulfinyl derivative of spiro-[fluoren-9,4'-imidazolidine]-2',5'-dione may be biotransformed in vivo to the corresponding more active methylthio derivative. There can be an interconversion of the sulfoxide to the sulfide by thioredoxin-dependent reductases and/or related glutaredoxins. In the converse, the methylthio derivative can be oxidized by cytochrome containing oxidoreductases to the corresponding methylsulfinyl derivative. These interconversions can be stereospecific with respect to the chirality of the resulting sulfoxide. Other sulfoxide or sulfinyl drugs such as Sulindac have been demonstrated to undergo these biotransformations as a function of drug intermediary metabolism. Therefore it is believed that the less in vitro active methylsulfinyl derivatives will exhibit greater than expected in vivo activity because of this intermediary metabolism.

In accordance with the present invention it has been found that compounds of the formulas: ##STR1## where x, y and z are hydrogen, halogen, methyl, amino, nitro, carboxy, methylthio, methylsulfinyl, methoxyl, methylsulfonyl and salts thereof with pharmacologically acceptable cations may be employed as aldose reductase inhibitors for the control and prevention of sorbitol levels in the sciatic nerve and lens of diabetics, to reduce sorbitol levels in the lens of glucosemic subjects with resulting control of diabetic complications including diabetic cataracts, and to generally treat diabetic complications including diabetic cataract, neuropathy, retinopathy and nephropathy.

Further in accordance with the present invention it has been found that the novel compounds having the formulas: ##STR2## where x is hydrogen, fluoro, methylthio, methylsulfinyl and methylsulfonyl and y is fluoro, methylthio, methylsulfinyl and methylsulfonyl and pharmaceutically acceptable salts thereof with pharmacologically acceptable cations may be employed as aldose reductase inhibitors for the control and prevention of sorbitol levels in the sciatic nerve and lens of diabetics, and to reduce sorbitol levels in the lens of glucosemic subjects with resulting control of diabetic complications including diabetic cataract, neuropathy, retinopathy, and nephropathy.

The pharmaceutically acceptable metallic salts can be prepared from the corresponding unneutralized derivatives using conventional methods. Treatment of a derivative with an aqueous solution of the desired pharmaceutically acceptable metallic hydroxide or other metallic base and evaporation of the resulting solution to dryness, usually under reduced pressure, will yield the salt. These compounds are unique over the prior art in that they contain a tricylic ring system which is rigid and planar in conjunction with a heterocyclic ring.

The substantial increase in activity and potency of the aforedescribed tetracyclic spiro-hydantoin derivatives as seen over known compounds by in vitro and in vivo assays is unanticipated. Prior art does not indicate such unanticipated increase in the activity and potency of such planar, rigid, tetracylic spiro-hydantoin derivatives. Further, the compounds are more active in vitro and in vivo than material found in the prior art and are anticipated to have characteristics that will provide useful in vivo human activity and potency. Furthermore, several of the potent symmetrically substituted derivatives do not require resolution as they are achiral.

It will be understood that these tetracylic spiro-hydantoin derivatives will contain an asymmetric center if the substitution pattern on rings A and C are not symmetric. It is known in the art that for this class of molecules, a resolved compound is more potent than an unresolved compound. For example, a 2-fluoro substitution renders the molecule asymmetric at the 9-position of the fluorene ring (the same carbon atom also may be designated to be at position 4' in the spiro hydantoin ring D). A 2,7-difluoro, 2,7-dibromo, 3,6 difluoro etc., substitution pattern results in a symmetric molecule and hence no resolution is needed for an increase in activity and potency.

It has also been found that tetracyclic spiro-xanthene-imidazolidines such as spiro-(2,7-difluroxanthen-9,4'-imidazolidine)-2',5'-dione and spiro-(xanthen-9,4'-imidazolidine)-2',5'-dione are unexpectedly less active as aldose reductase inhibitors and are not as potent as the corresponding tetracyclic fluorene compounds of the invention disclosed herein.

In accordance with the present process invention, a mono- or di-aminofluorene is reacted with fluoroboric acid and sodium nitrite to yield a mono- or di-diazonium fluoroborate salt which upon decomposition yields a mono- or di-fluorofluorene. The mono- or di-fluorofluorene is then oxidized to the ketone, a mono- or di-fluorofluorenone, by oxygen under basic conditions. Alternatively, this oxidation can be conducted with a more conventional oxidation method such as potassium permanganate in pyridine. This process may be illustrated as follows: ##STR3##

In accordance with this generalized scheme, 2-aminofluorene will yield 2-fluorofluorenone. This ketone, in a specific example of this generalized process, will upon treatment with ammonium carbonate and potassium cyanide in an alcohol, alcohol-and-water or acetamide solvent in a pressure reactor at elevated temperature with time will yield dl-spiro-(2-fluorofluoren-9,4'-imidazolidine)-2',5'-dione. A specific example in the process may be illustrated as follows: ##STR4##

Step 1 of the reaction is suitably carried out in aqueous solvent at cold temperature. The temperature is critical and should be controlled to less than 10° C. but above 0° C. for maximum result. In step 2 of the process the decomposition of the diazonium fluoroborate salt should be accomplished in an inert high boiling solvent such as xylenes.

Conversion of the fluorofluorene to the ketone in step 3 is accomplished by reacting a tetralkyl- or arylalkyl- trialkyl-ammonium hydroxide in an aprotic basic solvent, such as anhydrous pyridine, with the fluorofluorene to facilitate oxidation by oxygen. The oxygen can be atmospheric oxygen, but better results are obtained by bubbling pure oxygen into the reaction mixture, which excludes carbon dioxide, to generate the fluorofluorenone. The resulting ketone product can be purified by distillation in vacuo. Likewise to step 1, the ratio of reactants in the formation of the ketone is not critical as long as some excess ratio of equimolar amounts of the oxident is used. It is preferred to employ an excess of the tetralkyl- or arylalkyltrialkylammonium hydroxide to facilitate a more rapid oxidation. The temperature during this exothermic oxidation is preferably held at or below the reflux temperature of pyridine.

The ratio of reactants in step 4 of the reaction is important in the synthesis of the spiro-hydantoin product from the fluorofluorenone. Better results are obtained when the molar ratio or equivalents of potassium cyanide and ammonium carbonate are 1.5× to 3× and 2× to 5× in excess of the theoretical amount. The preferred solvent is absolute ethanol and the reaction is carried out at elevated temperatures under pressure. Other polar non-ketone or non-ester solvents such as acetamide or ethanol diluted with water can be employed. Purification can be accomplished by diluting the reaction mixture with acid, preferably dilute hydrochloric acid, and collecting the crude spiro-hydantoin precipitate. The base soluble and dimethylformamide soluble spiro-hydantoin can be purified through a series of activated charcoal treatments, filtration and reprecipitation procedures.

Examples L, M, S and U are given for purposes of illustrating the process invention (Examples L, M, P, Q, R, S, T and U also being given to illustrate the novel compositions of the invention) and such examples are not to be considered as limiting the invention.

PREPARATION A

Spiro-(fluoren-9,4'-imidazolidine)-2',5'-dione has the formula: ##STR5##

Spiro-[fluoren-9,4'-imidazolidine]-2',5'-dione was prepared by the general method of W. H. McCown and H. R. Henze as reported in J. Amer. Chem. Soc. 64, (1942) 689. Fluorenone (9 g, 50 mmol.), KCN (6.5 g, 100 mmol), ammonium carbonate (22.8 g) and 80% ethanol (100 mL) were placed in a 200 cc stainless steel reaction vessel. The mixture was heated at 115°-125° C. for 4.0 hours, cooled and diluted with ice cold 10% hydrochloric acid. The triturated solid was collected on the filter, washed with water and dried to yield 11.8 g (95%), m.p. 326°-329° C. dec. Recrystallization from ethanol yielded needles, m.p. 350°-353° C. dec., m/e⁺. 250 for C₁₅ H₁₀ N₂ O₂.

PREPARATION B

Spiro-[2,7-dichlorofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR6##

This compound was prepared by the method of Hsi-Lung Pan and T. L. Fletcher, J. Med. Chem. 10 (1967), 957-959. Spiro-[fluoren-9,4'-imidazolidine]-2',5'-dione (5 g, 20 mmol), FeCl₃ (0.5 g) and acetic acid (350 mL) was stirred at 75° C. while a solution of Cl₂ (3.6 g, 50 mmol) in acetic acid (60 mL) was added in one portion. The mixture was stirred with heat for twenty four hours. After cooling water was added and the product filtered. Recrystallization from ethanol gave 0.9 g of product (14%); m.p. 355°-358° C. dec.; m/e⁺. 318 for C₁₅ H₈ Cl₂ N₂ O₂.

PREPARATION C

dl-Spiro-[2-nitrofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR7## and may be prepared as follows.

Powdered spiro-[fluoren-9,4'-imidazolidine]-2',5'-dione (5.0 g, 20 mmol) was added to a stirred mixture of HNO₃ (2 g, 22 mmol) and 60% H₂ SO₄ (100 mL) at 5° C. Then the mixture was allowed to cool to room temperature and was stirred for twelve hours, ice water was added and the solid was filtered. Recrystallization from acetic acid gave a sample, m.p. 309°-312° C. dec., m/e⁺. 295 for C₁₅ H₉ N₃ O₄.

PREPARATION D

Spiro [2,7-dinitrofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR8##

It may be prepared according to Hsi-Lung Pan and T. L. Fletcher, J. Med. Chem 10, (1967) 957-959. Powdered spiro-[fluoren-9,4'-imidozolidine]-2',5'-dione (6.0 g) was added to a stirred mixture of HNO₃ (10 g) and 60% H₂ SO₄ (100 mL) at 50°-60° C. over a period of 45 minutes. The suspension was stirred at the same temperature for 5 hours and cooled. Cold water was added and the solid was filtered. Several recrystallizations from acetic acid gave a sample, m.p. 333°-335° C. dec., m/e⁺. 340 for C₁₅ H₈ N₄ O₆.

PREPARATION E

dl-Spiro-[2-bromofluoren-9,4'-imidazolidine]-2', 5'-dione has the formula ##STR9##

It may be prepared according to H. L. Pan and T. L. Fletcher, J. Med. Chem. 10, (1967) 957-959. 2-Bromofluorene (Trans World Chemicals, Inc.) was oxidized by sodium dichromate to 2-bromofluorenone. The product, yellow needles, recrystalized from ethanol gave a m.p. 146°-147° C. The ketone (2.6 g, 10 mmol), KCN (1.3 g, 20 mmol), ammonium carbonate (5.0 g) and 80% ethanol (100 mL) were placed in a stainless steel reaction vessel. The mixture was heated at 115°-125° C. for 4.0 hours. The product was collected as in Preparation A and recrystallized from ethanol to yield white needles (2.7 g), m.p. 350°-353° C., m/e⁺. 328 for C₁₅ H₉ BrN₂ O₂.

PREPARATION F

Spiro-[2,7-dibromofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR10## and may be prepared as follows.

To 2,7-dibromofluorene (1.5 g, 4.6 mmol) in pyridine (50 mL) was added potassium permanaganate (0.73 g, 4.6 mmol) and the mixture was stirred overnight. Alcohol (10 mL) was added and then water 100 ml and the mixture was extracted with ether (100 mL, twice). The combined extracts were washed with two portions of 5% hydrochloric acid (20 mL each) and water (50 ml). The ether was evaporated to yield 1.2 g of the ketone needles from benzene, m/e⁺. 334 for the ketone, m.p. 196°-197° C. for C₁₃ H₆ Br₂ O. The ketone (1.2 g, 3.6 mmol), KCN (0.468, 7 mmol) and ammonium carbonate (1.36 g) in alcohol (15 mL) were heated at 105° C. overnight in a stainless steel pressure reactor. The product was collected as in Procedure A, the product having a m.p. 340° C., m/e⁺. 406 for C₁₅ H.sub. 8 N₂ O₂ Br₂.

PREPARATION G

dl-Spiro-[4-aminofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR11## and may be prepared as follows.

4-Amino-fluorenone (Pfaltz and Bauer, Inc.) (5 g, 19 mmol), KCN (3.33 g, 51 mmol), ammonium carbonate (9.9 g) in 95% alcohol (50 mL) were heated in a glass pressure reactor at 105° C. for 24 hours. The cooled reaction mixture was poured into 400 ml cold water and adjusted to pH 5 with hydrochloric acid. The precipitate was filtered and redissolved in 5% NaOH pressure reactor at 105° C. for 24 hours. The cooled reaction mixture was poured into 400 ml cold water and adjusted to pH 5 with hydrochloric acid. The precipitate was filtered and redissolved in 5% NaOH solution (100 mL) and refiltered through a Celite pad. Once again the pH was adjusted to an acid pH and the solid collected; recrystallization from hot methanol yielded a product m.p. 340°-342° C.; m/e⁺. 265 for C₁₅ H₁₁ N₃ O₂.

PREPARATION H

dl-Spiro-[2-aminofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR12## and may be prepared as follows.

2-Aminofluorenone (Aldrich Chemical Co., Inc.) (1.95 g, 10 mmol), KCN (1.0 g, 15 mmol), ammonium carbonate (2.0 g) and 90% ethanol (50 mL) were heated in a glass pressure reactor at 105° C. for 24 hours. The cooled reaction mixture was poured into 100 mL cold water and the pH was adjusted to 5 with 10% hydrochloric acid; the precipitate was filtered and redissolved in 5% NaOH (50 mL) and refiltered. Once again the pH was adjusted to an acid pH and solid collected. Recrystallization from hot methanol yielded a product m.p. 310°-314° C. m/e⁺. 265 for C₁₅ H₁₁ N₃ O₂.

PREPARATION I

Spiro-[2,7-diaminofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR13## and may be prepared as follows.

Spiro-[2,7-dinitrofluoren-9,4'-imidazolidine]-2',5'-dione (4.5 g, 13 mmol) was suspended in 1 liter reagent alcohol. A stirred suspension of 85% hydrazine hydrate (25 mL) and Raney nickel (1 g) was added. The mixture was refluxed for two hours and filtered. The filtrate was evaporated to yield a light brown solid. The product was recrystallized from ethanol, m.p. 340°-344° C. dec., m/e⁺. 280 for C₁₅ H₁₂ N₄ O₂ ; HRMS for C₁₅ H₁₂ N₄ O₂ : calc. 280.0960, obs. 280.0951, error 0.9 mmu/3.2 ppm.

PREPARATION J

dl-Spiro-[2-iodofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR14## and may be prepared as follows.

2-Iodofluorenone (Aldrich Chemical Co.) (4.0 g, 13 mmol), KCN (1.7 g, 30 mmol), ammonium carbonate (6.0 g) in 90% ethanol (60 mL) was placed in a stainless steel reaction vessel. The mixture was heated at 110°-115° C. for 12 hours. The reaction vessel was cooled, and cold 10% hydrochloric acid was added. The precipitate was collected by filtration. The solid was dissolved in 5% sodium hydroxide and reprecipitated with cold 10% hydrochloric acid. The collected solid was recrystallized from acetone and water to yield fine crystals, m.p. 358°-359° C., m/e⁺. 376 for C₁₅ H₉ IN₂ O₂. 13 mmol), KCN (1.7, 30 mmol), ammonium carbonate (6.0 g) in 90% ethanol (60 mL) was placed in a stainless steel reaction vessel. The mixture was heated at 110°-115° C. for 12 hours. The reaction vessel was cooled, and cold 10% hydrochloric acid was added. The precipitate was collected by filtration. The solid was dissolved in 5% sodium hydroxide and reprecipitated with cold 10% hydrochloride acid. The collected solid was recrystallized from acetone and water to yield fine crystals, m.p. 358°-359° C., m/e⁺. 376 for C₁₅ H₉ IN₂ O₂.

PREPARATION K

dl-Spiro-[1-methylfluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR15## and may be prepared as follows.

1-Methylfluorenone (2 g, 13 mmol), KCN (1.7 g, 26 mmol), ammonium carbonate (5.1 g) and 95% ethanol (50 mL) were placed in a glass pressure reactor and heated overnight. The reaction mixture was diluted with 200 mL 5% hydrochloric acid solution and the product was collected on a filter. The product was then dissolved in 5% NaOH solution (150 mL); refiltered; reprecipitated with conc. hydrochloric acid. This product was recrystallized from hot methanol; yield 1.5 g; m.p. 334°-336° C. dec.; m/e⁺. 264 for C₁₆ H₁₂ N₂ O₂.

PREPARATION L

dl-Spiro(2-fluorofluoren-9,4'-imidazolidine)-2',5'-dione has the formula: ##STR16##

Fluoroboric acid (3000 ml, 48-50%) is diluted with water (1500 mL) and chilled. 2-Aminofluorene (Aldrich Chemical Co.) (543.7 g, 3 mol) in tetrahydrofuran (1500 ml) was portion wise added with stirring to the chilled fluorboric acid solution (4500 mL). A pink-brown solid formed during addition. The mixture was stirred until it became homogeneous and then was chilled to approximately 5° C. with a dry ice in an acetone bath. A saturated aqueous solution of sodium nitrite (300 g with water to yield 600 cc of solution) was added dropwise while at 3°-8° C. After the addition, the mixture was stirred for one hour. The insoluble green product was collected by filtration and washed with 5% flouroboric acid (3×200 mL), methanol (300 mL), 15% methanol in ether (5×200 mL), ether (5×200 mL) and then air dried overnight to yield the diazonium salt (809 g, 97%), m.p. 133°-135° dec. The diazonium salt (800 g) was suspended in xylenes (3000 mL) with stirring. The mixture was heated to boiling. As the temperature became 100° C. nitrogen gas evolved and subsided as the temperature became 135° C. The boiling mixture was filtered hot through a Celite (a diatomaceous filter aid) pad and the pad was washed with hot xylenes (3×200 mL). The combined filtrates were evaporated in vacuo with heat to dryness. The residue was dissolved in boiling hexanes (3000 mL) then filtered through a Celite and Norite (neutralized charcoal) filter pad with hot hexanes wash (400-600 mL). The combined hexanes filtrates then were cooled with dry ice. The resulting white precipitate was collected by filtration. The collected product was washed with cold hexanes (200 mL), suction dried and oven dried at 50° C. to yield 2-fluorofluorene (380 g, 71.7%) with a m.p. 97.5°-98.0° C. A second crop of product was collected by concentrating the hexanes mother liquor, cooling and collecting the precipitate as before (total combined yield 416 g).

2-Fluorofluorene (824.7 g, 4.48 mol) was dissolved in pyridine (4 L) and stirred. A 40% solution of Triton B (100 mL of benzyltrimethylammonium hydroxide 40% in pyridine according to a general procedure of U. Sprinzak, J. Amer. Chem. Soc. 80 (1958) 5449) was added and oxygen was bubbled into the vigorously stirred solution. This exothermic reaction was run for 20 hours whereupon an additional portion of the Triton B solution (50 mL) was added with continued stirring and oxygen addition for an additional 24 hours. The resulting dark green reaction mixture was treated with Norite (100 g, neutralized charcoal), stirred for 30 minutes and filtered through a Celite pad (diatomaceous earth filter aid). The filter pad was then washed with pyridine (1 L). The combined filtrates were concentrated to a small volume in vacuo with heat. A 5% solution of hydrochloric acid in water (1 L) was added and the pyridine was azeotrophed in vacuo with heat. This process was repeated until a total of 6-8 L of water were evaporated. The granular product was filtered and washed with water (4 L) and air dried. The yellow-orange product was melted and distilled through a large bore short path distillation apparatus (bp 167°-170° C.; 1.5 mm Hg) to yield into a chilled receiving flask the bright yellow 2-fluorofluorenone (600 g) with a m.p. 113°-115° C. and m/e⁺. 198 for C₁₃ H₇ FO.

2-Fluorofluorenone (300 g, 1.52 mol), ammonium carbonate (420 g) and potassium cyanide (120 g, 1.84 mol) were suspended in absolute ethanol (1.2 L) in a 2 L stainless steel Parr pressure reaction apparatus. The sealed vessel was heated at 95°-100° C. with mechanical stirring over 42-46 hours. The contents of the 2 L vessel was transferred into water (4 L). The yellowish water mixture was made acidic by the slow addition of concentrated hydrochloric acid (500 mL) so as to be pH2. The resulting precipitate was collected by filtration, washed with water (4 L) and suction dried. The damp solid was partially solubilized with 1N sodium hydroxide (1.5 L) by stirring. The insolubles were removed by filtration through a Celite filter aid and neutralized charcoal pad to obtain a clear solution. The pad was washed with 1N sodium hydroxide (1.0 L). The combined filtrates were acidified as before with conc. hydrochloric acid (about 200 mL) to pH2. The white precipitate was collected by filtration, washed with water (4 L), suction dried, and washed with ether (4×300 mL). The damp solid then was dried at 100° C. for 12 hours to yield dl-spiro-(2-fluorofluoren-9,4'-imidazolidine)-2',5'-dione (301 g, 74.3%), 284 g of this product was dissolved in dimethylformamide (600 mL) at 40° C. Norite (40 g, neutralized charcoal) was added to the solution and the mixture stirred at 45° C. for 40 min. The mixture was filtered through a Celite pad and the filtrate was diluted with water (2 L). The solid was collected by filtration with water wash (500 mL). The damp solid was dissolved in 1N sodium hydroxide (1 L) and treated with Darco G-60 (Fisher Scientific activated charcoal for chromatography) and stirred for 35 min. at 30° C. The mixture was filtered through a carefully prepared Celite pad with 1N sodium hydroxide solution wash (500 mL) and water wash (1 L). The combined filtrates (2.5 L) were neutralized with concentrated hydrochloric acid to pH 6.5. The white precipitate was collected by filtration and was washed with water, air dried and oven dried at 100° C. for 24 hrs. to yield (273 g) of dl-spiro-(2-fluorofluoren-9,4'-imidazolidine)-2',5'-dione.

A sample of the product, which was recrystallized from ethanol, gave a m.p. 315° C. with decomposition, HRMS analysis for C₁₅ H₉ FN₂ O₂ calc. 268.0648, obs. 268.0659; error 1.1 mmu/4.1 ppm; C₁₅ H₉ FN₂ O₂, calc %C 67.15 %H 3.38 %N 10.45 %F 7.08, obs. %C 67.24 %H 3.56 %N 10.42 %F 7.22, obs. %C 67.17 %H 3.42 %N 10.41 %F 6.98, obs. %C 67.29 %H 3.47 %N 10.50 %F 7.27, obs. %C 67.26 %H 3.35 %N 10.41 %F 7.03; IR Spectrum: 3270 cm⁻¹ N--H stretch of II° imide, 3170 cm⁻¹, N--H stretch of imide, 3050 cm⁻¹, Sp² C--H stretch, 1775 cm⁻¹, C═O stretch of imide, 1715 cm⁻¹ C═O stretch of imide and amide, 1610, 1590, 1495 and 1455 cm⁻¹ aromatic in-plane carbon stretching modes, 1422 cm⁻¹ N--H in-plane bend of II° cyclic amide, 868, 830 and 752 cm⁻¹ aromatic C--H out-of-plane deformation, and NMR Spectrum Assignments: delta 11.3 ppm: broad singlet, 1H, imide proton; 8.7 ppm: broad singlet, 1H, amide proton; 7.9 ppm: multiplet, 2H, aromatic protons; 7.4 ppm: multiplet, 5H, aromatic protons.

PREPARATION M

Spiro-[2,7-difluorofluoren-9,4'-imidazolidine]-2',5'-dione has the formula: ##STR17## can be prepared from 2,7-difluorofluorene which can be obtained from the Alfred Bader Library of Rare Chemicals. Alternatively, 2,7-difluorofluorene may be prepared in accordance with the following procedure. To 2, 7-diaminofluorene (Aldrich Chemical Co.) (4.98 g, 25.4 mmol) in tetrahydrofuran (90 mL) was added water (25 ml) and fluoroboric acid (48-50%, 50 mL). A thick paste of the fluoroborate salt formed. While stirring and cooling (5° C.), a saturated aqueous solution of sodium nitrite (5 g) was added dropwise while maintaining the temperature at 5°-10° C. After addition, the mixture was stirred for ten minutes and filtered and washed with 5% fluoroboric acid, methanol and then ether. The dried product, the bis-diazonium salt, decomposed at 127° C. The salt product was then mixed with boiling xylenes (50 mL) and heated for 30 minutes yielding a dark tar material, 5.1 g. The tar was isolated and triturated with ether. The ether was evaporated and the product, 2,7-difluorofluorene, was recrystallized from ethanol, 3.9 g, m.p. 80°-82.5° C. The 2,7-difluorofluorene (2 g, 10 mmol) was dissolved in pyridine (30 mL) and potassium permanganate (1.58 g) was added and stirred at room temperature overnight. The reaction mixture was diluted with water and then acidified with 5% HCl. The solid was filtered and water washed. The solid was suspended in 100 mL water and a solution of saturated sodium bisulfite and concentrated hydrochloric acid (7.27 g NaHSO₃, 6.90 g of conc. HCl) was added and the mixture stirred for thirty minutes. The solid was collected by filtration and then dissolved in ether and refiltered. The ether extracted ketone product 2,7-difluorofluorenone (0.9 g) gave m/e⁺. 216.

2,7-Difluorofluorenone (43.2 g, 0.2 mol), KCN (16.93 g, 0.26 mol), ammonium carbonate (40.59 g, 0.52 mol) and alcohol were reacted at 90°-110° C. for 71 hours. The workup on the hydantoin was in accordance with procedure L. Recrystallization of the acid insoluble product from methanol and acetone was followed by a base solubilization and acid precipitation yield of spiro-[2,7-difluorofluoren-9,4'-imidazolidine]-2',5'-dione (32.8 g, 0.115 mol), m/e⁺. 286 for C₁₅ H₈ F₂ N₂ O₂ ; m.p. 327°-329° dec.; and Calc. %C 62.94 %H 2.82 %F 13.28 %N 9.79, Obs. %C 62.78 %H 2.86 %F 13.05 %N 9.62.

PREPARATION N

dl-Spiro-[2-carboxyfluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR18## and may be prepared as follows.

2-Carboxyfluorenone (2.5 g, 11.2 mmol), KCN (1.5 g, 23 mmol), ammonium carbonate (4.4 g) and alcohol (50 mL) were heated at 105° C. in a glass pressure reactor overnight. The reaction mixture was poured into 5% HCl (100 mL) and the product filtered. The collected product was dissolved in 5% NaOH, refiltered and precipitated with acid. The filtered precipitate was washed with water and air dried having a m.p. 331°-332° C. dec., C₁₆ H₁₀ N₂ O₄ m/e⁺. 294.

PREPARATION O

dl-Spiro-[3-chlorofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR19## and may be prepared as follows.

N-2-(3-chloro-9-oxofluorenyl)-trifluoroacetamide was prepared according to the procedure of H. Pan and T. L. Fletcher in J. Med. Chem. 7, (1964) 31-38. This ketone (3.25 g, 10 mmol) was refluxed in 20% hydrochloric acid (100 mL) for one hour and then cooled to 5° C. The amine was then diazotized with sodium nitrite (1.0 g, 1.5 equivalents). Cold 50% hypophosphorus acid (100 mL) then was slowly added. The mixture then was stored overnight at 5° C., then warmed to ambient temperature, diluted with water and extracted with benzene. Chromatography through alumina with benzene as an eluent yielded 3-chlorofluorenone (1.6 g). Yellow plates from ethanol had a m.p. 156°-158° C.; HRMS calc. 214.0185 for C₁₃ H₇ ClO, obs. 214.0188, error 0.3 mmu/1.4 ppm.

The ketone (1.5 g, 7 mmol), KCN (0.65 g, 10 mmol), ammonium carbonate (1.5 g) and 90% ethanol (60 ml) was placed in a stainless steel reaction vessel. The mixture was heated at 110°-115° C. for 12 hours. The reaction vessel was cooled and cold 10% hydrochloric acid was added. The triturated solid was collected by filtration. The resulting solid was dissolved in 5% sodium hydroxide, filtered and the filtrate was acidified with concentrated hydrochloric acid. The precipitated solid was collected by filtration and washed with cold water (1.1 g) yielding a product with a m.p. 330° C. dec., HRMS calc. 284.0352 for C₁₅ H₉ ClN₂ O₂, obs. 284.0364, 1.1 mmu/4.2 ppm.

PREPARATION P

dl-Spiro-[2-methylthiofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR20## and may be prepared as follows.

The ketone, 2-methylthiofluorenone, was prepared by suspending sodium hydride (14.4 g of the 50% by weight mineral oil dispersion, 0.30 mol) in anhydrous dimethylformamide (400 mL). To this stirred suspension under an argon atmosphere was added methylmercaptan as a gas. After the solution was saturated with methylmercaptan and the sodium hydride reacted, the yellow 2-fluorofluorenone (30 g, 0.15 mol) was added in one portion. The resulting red solution was heated for four hours at 60°-80° C. Water (50 mL) was added and the solvent was removed with heat and reduced pressure. The red residue was dissolved in ethyl acetate (500 mL) and extracted with 0.1N sodium hydroxide (3×200 mL). These extractions were followed by washes with 0.1N hydrochloric acid (200 mL) and water (3×200 mL). The yellow-orange ethyl acetate solution then was treated with activated charcoal and anhydrous sodium sulfate. After filtration the ethyl acetate solution was evaporated with heat and reduced pressure to yield an orange solid which was triturated with hot hexanes (200 mL) and then allowed to cool. The ketone was collected by filtration (31.1 g, 91%), the product having a m.p. of 85° C. (reported 84°-85° C. by J. A. Parry and K. D. Warren, J. Chem. Soc. 1965, 4049-4054); PMR (CDCl₃, TMS): delta 2.4 (3H, methyl singlet); delta 6.95-7.7 (7H, aromatic multiplet); and m/e⁺. 226 for C₁₄ H₁₀ OS.

The ketone (22.6 g, 0.10 mol), KCN (13 g, 0.20 mol), ammonium carbonate (30 g) and absolute ethanol (approx. 120 mL) were heated in a 200 cc stainless steel pressure reactor for 15 hours at 105° C. After cooling the contents were poured with stirring onto ice (200 cc) and 5N hydrochloric acid (100 mL). The resulting orange suspension then was collected by filtration onto sintered glass. Then 1N sodium hydroxide (250 mL) was filtered with stirring through the collected solid. The bright orange filtrate then was precipitated with concentrated hydrochloric acid and collected. The air dried precipitate then was dissolved in hot dimethylformamide (100 mL). The solution was treated with Darco G-60 (activated charcoal sold by Fischer Scientific Products for chromatography, 4 g) and filtered with the aid of Celite. Water (400 ml) and ice (100 cc) were added to the filtrate precipitating an off-white solid.

The collected precipitate was then redissolved in 1N sodium hydroxide and treated as before with Darco G-60. After acidification the resulting white precipitate was collected and washed thoroughly with water and dried at 100° C. in a vacuum oven to yield dl-spiro-[2-methylthiofluoren-9,4'-imidazolidine]-2',5'-dione (18.6 g., 63%) with a m.p. 299°-300° C. dec.; HRMS for C₁₆ H₁₂ N₂ O₂ S calc. 296.0619, obs. 296.0626, error 0.7 mmu/2.4 ppm; and PMR (DMSO-d6, TSP); delta 2.47 (3H, methyl); delta 7.0-8.8 (9H, aromatic and hydantoin multiplet); and elemental analysis: calc. %C 64.85%H 4.08%N 9.45%S 10.82. obs. %C 64.89%H 4.12%N 9.44%S 10.95.

PREPARATION Q

Spiro-[2-(R,S)-methylsulfinylfluoren-9, (R,S)-4'-imidazolidine]-2',5'-dione has the fomula ##STR21## and the unresolved diastereomeric mixture of the four stereoisomers [(R,R), (R,S), (S,S), (S,R) isomers] may be prepared as follows.

The hydantoin product of procedure P(3.0 g, 10 mmol) was suspended in 50% acetone and water (100 mL) and sodium metaperiodate (2.25 g, 10.5 mmol) was added. This mixture was stirred at ambient temperature for 72 hours, whereupon 100 mL of 1N hydrochloric acid were added and the suspension was filtered and washed thoroughly with water. The resulting solid was dissolved in 1N NaOH (25 mL), filtered and the filtrate acidified with concentrated hydrochloric acid. Filtration and water washes yielded a white product (2.6 g, with drying at 100° C.) with a m.p. 284°-286° C. dec.; HRMS for C₁₆ H₁₂ N₂ O₃ S calc. 312.0568 obs. 312.0565 error 0.3 mmu/1.0 ppm; and PMR (DMSO-d6, TSP): delta 2.84 (3H, methyl singlet), (9H, low field aromatic and hydantoin multiplet).

PREPARATION R

dl-Spiro-(2-methylsulfonylfluoren-9,4'-imidazolidine)-2',5'-dione has the formula ##STR22## and may be prepared as follows.

The hydantoin product of procedure P (3.0 g, 10 mmol) was suspended in 50% acetone and water (100 mL), and sodium metaperiodate (6.42 g, 30 mmol) was added. This mixture was refluxed with stirring for 15 hours, whereupon 100 mL of 1N hydrochloric acid and 100 cc of ice were added. The suspension was filtered and washed thoroughly with water and air dried. Further drying in a vacuum oven at 100° C. yielded a white fluffy product (3.1 g) with a m.p. 309°-311° C. dec.; HRMS for C₁₆ H₁₂ N₂ O₄ S calc. 328.0518, obs. 328.0527 error 0.9 mmu/2.7 ppm; and PMR (DMSO-d6, TSP): delta 3.30 (3H, methyl singlet); (9H, low field aromatic and hydantoin multiplet).

PREPARATION S

dl-Spiro-[1-fluorofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR23## and may be prepared as follows.

1-Fluorofluorenone was prepared from 1-aminofluorenone (Pfaltz and Bauer, Inc.) by the procedure of T. L. Fletcher and M. J. Namkung, Chemistry and Industry, Feb. 11, 1961, pp. 179-180 which yielded a ketone product m.p. 109°-110° C., m/e⁺. 198 for C₁₃ H₇ FO.

1-Fluorofluorenone (3.96 g, 20 mmol), KCN (1.95 g, 30 mmol), ammonium carbonate (4.8 g) and 100% ethanol (100 ml) were reacted and a product (2.8 g) collected as in Preparation L, the product having a m.p. 338°-341° C. dec., HRMS for C₁₅ H₉ FN₂ O₂ calc. 268.0648, obs. 268.0653 error 0.5 mmu/1.9 ppm.

PREPARATION T

dl-Spiro-[3-fluorofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR24## and may be prepared as follows.

3-Fluorofluorenone was prepared from 3-aminofluorenone by the procedure of T. L. Fletcher and M. J. Namkung, Chemistry and Industry, Feb. 11, 1961, pp. 179-180 and T. L. Fletcher et. al., J. Org. Chem., 25, (1960) 1342 yielding the ketone product with a m.p. 129° C. and m/e⁺. 198 for C₁₃ H₇ FO. The preparation of the spiro hydantoin was otherwise as in Preparation L, (yield 3.1 g) the resulting product with a m.p. 328°-332° C. dec., and HRMS for C₁₅ H₉ FN₂ O₂ calc. 268.0648, obs. 268.0653, error 0.5 mmu/1.9 ppm.

PREPARATION U

dl-Spiro-[4-fluorofluoren-9,4'-imidazolidine]-2',5'-dione has the formula ##STR25## and may be prepared as follows.

4-Flourofluorenone was prepared from 4-aminofluorenone (Pfaltz and Bauer, Inc.) by the procedure of T. L. Fletcher and M. J. Namkung, Chemistry and Industry, Feb. 11, 1961, pp. 179-180 yielding the ketone product with a m.p. 160°-162° C. and m/e⁺. 198 for C₁₃ H₇ FO. The preparation of the spiro hydantoin was otherwise as in Preparation L (yield 3.0 g), the resulting product with a m.p. 330°-333° C. and HRMS for C₁₅ H₉ FN₂ O₂ calc. 268.0648, obs. 268.0660, error 1.2 mmu/4.5 ppm.

PREPARATION V

dl-Spiro-(4-aza-fluorene-9,4'-imidazolidine)-2',5'dione has the formula: ##STR26## and may be prepared as follows.

4-Aza-9-fluorenone (Aldrich Chemical Co.), (2.4 g, 13.3 mmol), KCN (2.0 g, 30.7 mmol) and ammonium carbonate (5.0 g) in 80% ethanol (50 cc) were placed in a thick walled glass pressure reactor. The mixture was heated at 110°-115° C. for 12 hours. The reaction vessel was cooled and ice water (200 mL) was added to the reaction mixture. Dilute hydrochloric acid was added until pH was approximately 8 and the solid was collected by filtration. The collected solid was dissolved in 5% sodium hydroxide and treated with activated charcoal and filtered through a Celite (diatomaceous earth filter aid) pad. The solution was adjusted to pH 7-8 by the addition of 1N hydrochloric acid. The resulting precipitate was collected on a filter, washed with cold water and dried to yield a sample of dl-spiro-(4-azafluorene-9,4'-imidazolidine)-2',5'-dione (1.4 g) having a melting point of 311°-312° C. with dec., m/e⁺ . 251 for C₁₄ H₉ N₃ O₂.

Preparations of dl-Spiro-(1,7-difluoro fluoren-9,4'-imidazolidine)-2',5'-dione; dl-spiro-(2,5-difluorofluoren-9,4'-imidazolidine)-2',5'-dione, dl-spiro-(2,6-difluorofluoren-9,4'-imidazolidine)-2',5'-dione; spiro-(2-fluoro-7-methylthiofluoren-9,4'-imidazolidine)-2',5'-dione; and spiro-(2-fluoro-7-methylsulfinylfluoren-9,4'-imidazolidine)-2',5'-dione

dl-Spiro-(1,7-difluorofluoren-9,4'-imidazolidine)-2',5'-dione can be prepared from 1-fluorofluorene. dl-Spiro-(2,5-difluorofluoren-9,4'-imidazolidine)-2',5'-dione can be prepared from 4-fluorofluorene. dl-Spiro-(2,6-difluorofluoren-9,4'-imidazolidine)-2',5'-dione can be prepared from 3-fluorofluorene. These fluorene precursors, 1-fluorofluorene, 4-fluorofluorene and 3-fluorofluorene can be prepared via the Schiemann reaction from the corresponding amines, 1-aminofluorene, 4-aminofluorene and 3-aminofluorene, according to the procedure of T. L. Fletcher and M. L. Namkung, Chemistry and Industry, Feb. 11, 1961, pp. 179-180. The resulting 1-fluorofluorene, 4-fluorofluorene and 3-fluorofluorene derivatives can be nitrated in the 7 position using the general nitration method cited in Org. Synthesis, Coll. Vol. 2, 447 (1943). The resulting nitro derivatives, 1-fluoro-7-nitrofluorene, 4-fluoro-7-nitrofluorene and 3-fluoro-7-nitrofluorene, can be reduced using the general reduction method cited in Org. Synthesis, Coll. Vol 5, 30 (1973) to yield 7-amino-1-fluorofluorene, 2-amino-5-fluorofluorene and 2-amino-6-fluorofluorene respectively. These amines employing the general procedure of T. L. Fletcher and M. L. Namkung, Chemistry and Industry, Feb. 11, 1961, pp. 179-180 can be transformed via the corresponding diazonium tetrafluoroborate salts into 1,7-difluorofluorene, 2,5-difluorofluorene and 2,6-difluorofluorene. These difluorofluorenes can be oxidized to the corresponding ketones using a general procedure of U. Sprinzak, J. Amer. Chem. Soc., 80 (1958) or via procedures cited herein in Procedure L or M to yield: 1,7-difluorofluorenone; 2.5-difluorofluorenone; 2,6-difluorofluorenone. As in procedures L and M these ketones can be converted into the corresponding spiro-hydantoins:

dl-spiro-(1,7-difluorofluoren-9,4'-imidazolidine) -2',5'-dione; dl-spiro-(2,5-difluorofluoren-9,4'-imidazolidine)-2',5'-dione; dl-spiro-(2,6-difluorofluoren-9,4'-imidazolidine)-2',5'-dione respectively.

dl-Spiro-(2-fluoro-7-methylthiofluoren-9,4'-imidazolidine)-2',5'-dione can be prepared from 2,7-difluorofluorenone. The 2,7-difluorofluorenone is reacted as in Procedure P except one equivalent of the sodium methylthiolate (prepared from sodium hydride and methylmercaptan)is employed. The resulting 2-fluoro-7-methylthiofluorenone is synthetically transformed as in procedure L or P to the desired racemic spiro-(2-fluoro-7-methylthiofluoren-9,4'-imidazolidine)-2',5'-dione.

The diastereomeric mixture of four stereoisomers of spiro-(2-fluoro-7-methylsulfinylfluoren-9,4'-imidazolidine)-2',5'-dione can be prepared according to the Procedure Q cited herein whereby racemic spiro-(2-fluoro-7-methylthiofluoren-9,4'-imidazolidine)-2',5'-dione is oxidized by sodium metaperiodate to yield the diastereomeric mixture of four stereoisomers of spiro-(2-fluoro-7-methylsulfinylfluoren-9,4'-imidazolidine)-2',5'-dione.

Compounds A to U were tested for their ability to inhibit aldose reductase enzyme activity via the procedure of P. F. Kador, L. O. Merola and J. H. Kinoshita as described in Documenta Ophthamologica, 18 (1979) 117. The results are shown in Table I, II and III.

                  TABLE I                                                          ______________________________________                                         IC*.sub.50 -Human Aldose Reductase Inhibition Activity                         COMPOUND         IC.sub.50 (Molar)                                             ______________________________________                                         A (unsubstituted)                                                                               1.2 × 10.sup.-6                                         L (dl-2-Fluoro)  9.1 × 10.sup.-8                                         M (2,7-Difluoro) 5.2 × 10.sup.-8                                         Sarges Resolved**                                                                               6.4 × 10.sup.-7                                         ______________________________________                                          *IC.sub.50 = Concentration of drug that inhibits 50% of the enzyme             activity                                                                       **Sarges Resolved Compound =                                                   dSpiro-(6-fluorochroman-4,4imidazolidine)-2',5dione.                     

                  TABLE II                                                         ______________________________________                                         IC*.sub.50 -Rat Aldose Reductase Inhibition Activity                           COMPOUND          IC.sub.50 (Molar)                                            ______________________________________                                         L (dl-2-Fluoro)   1.5 × 10.sup.-7                                        M (2,7-Difluoro)  4.4 × 10.sup.-8                                        P (dl-2-Methylthio)                                                                              4.2 × 10.sup.-7                                        Q (dl-2-Methylsulfinyl)                                                                          1.7 × 10.sup.-6                                        R (dl-2-Methylsulfonyl)                                                                          5.0 × 10.sup.-6                                        S (dl-1-Fluoro)   5.9 × 10.sup.-7                                        U (dl-4-Fluoro)   4.6 × 10.sup.-7                                        Sarges Racemic**  4.3 × 10.sup.-7                                        Sarges Resolved***                                                                               1.5 × 10.sup.-7                                        ______________________________________                                          *IC.sub.50 = Concentration of drug that inhibits 50% of the enzyme             activity.                                                                      **Sarges Racemic Compound =                                                    dlSpiro-(6-fluorochroman-4,4imidazolidine)-2',5dione.                          ***Sarges Resolved Compound =                                                  dSpiro-(6-fluorochroman-4,4imidazolindine)-2',5dione.                    

It is noteworthy that Compounds L and M are as active or more active against human aldose reductase than rat aldose reductase and hence more selective against human aldose reductase than rat aldose reductase when compared to the Sarges resolved compound. These agents will exhibit more activity in humans than the Sarges resolved compound. The Sarges resolved compound shows only one fourth as much activity against human aldose reductase as compared to its activity against rat aldose reductase. It is apparent on analysis of both in vitro and in vivo potency data described herein that compounds L and M will exhibit significantly greater relative potencies in humans against aldose reductase related diabetic complications. This is apparent from comparative studies cited herein on diabetic and glactosemic rats and in vitro human enzyme inhibition studies. Both the racemic 2-fluoro (L) and 2,7-difluoro (M) derivatives are 7X and 12X more active against human aldose reductase than the Sarges resolved compound. The Sarges resolved compound is found to be equiactive against rat aldose reductase to the racemic 2-fluoro and half as active as the 2,7-difluoro derivative in vitro, but both the 2-fluoro and 2,7-difluoro derivatives were found unexpectedly and significantly more active in vivo than the Sarges compound in rat studies.

                  TABLE III                                                        ______________________________________                                         In vitro Aldose Reductase Inhibition:*                                         IC.sub.50                                                                            10.sup.-4                                                                               10.sup.-5                                                                             10.sup.-6                                                                             10.sup.-7                                                                           10.sup.-8                                                                             Species                               ______________________________________                                         A     89       84     49     13   --     Human                                 B     65       30     12     --   --     Human                                 C     65       20      8     --   --     Human                                 D     100      76     20     --   --     Human                                 E     100      82     62     33    8     Rat                                   F     --       94     76     55   12     Rat                                   G     50       28     20     --   --     Human                                 H     43       31      0     --   --     Human                                 I     50       25     10     --   --     Human                                 J     94       88     77     39    0     Human                                 K     96       85     47      6   --     Rat                                   L     100      88     81     53   18     Human                                 M     --       81     71     64   35     Human                                 N     89       54      0     --   --     Rat                                   ______________________________________                                          *According to the procedures of P. F. Kador and N. E. Sharpless,               Biophysical Chemistry, 8 (1978) 81-85; P. F. Kador, L. O. Merola and J. H      Kinoshita Documenta Ophthamologica, 18 (1979) 117.                       

In Vivo Evaluations

A. The effect of dl-spiro-(2-fluoro-fluoren-9,4'-imidazolidine)-2',5'-dione and spiro-(2,7-difluoro-fluoren-9,4'-imidazolidine)-2',5'-dione on the prevention on retardation of cataracts in rats was studied using the unresolved dl-spiro-(6-fluorochroman-4,4'-imidazolidine)-2',5'-dione based upon Sarges 4,117,230. The compounds were formulated in ground Purina Rodent Laboratory Chow, Number 5001, containing 30% galactose.

Eighty-four rats were divided into the following seven groups (six treated groups having different compound intake levels and an untreated galactose control) having different compound intake levels as shown in Table IV.

                  TABLE IV                                                         ______________________________________                                         Test Compound Dosages                                                                          Mg INTAKE/Kg                                                   COMPOUND        BODYWEIGHT/DAY                                                 ______________________________________                                         L (2-fluoro) Racemic                                                                           4 Mg/Kg/day                                                    L (2-fluoro) Racemic                                                                           8 Mg/Kg/day                                                    M (2,7-difluoro)                                                                               4 Mg/Kg/day                                                    M (2,7-difluoro)                                                                               8 Mg/Kg/day                                                    Sarges Racemic  4 Mg/Kg/day                                                    Sarges Racemic  8 Mg/Kg/day                                                    Galactose CONTROL                                                                              --                                                             ______________________________________                                    

The galactose control group (twelve rats, twenty-four eyes) were fed ground Purina Rodent Laboratory Chow, No. 5001 containing 30% by weight galactose. The six test compound groups (twelve rats, twenty-four eyes per group) were fed the same 30% galactose chow except that the chow was formulated to deliver mg/kg/day of the indicated test compound (see Table IV).

It is known that young male rats fed a 30% galactose diet (As previously described) will develop lenticular changes within several days which predicatively progress in time irreversibly to cataracts. Aldose reductase inhibitor compounds which are in vivo active will delay or prevent galactose induced cataractogenesis. In this in vivo experiment, the test aldose reductase inhibitor compounds were formulated in the 30% galactose feed to evaluate their in vivo anticataract activity. The 168 rat eyes of the eighty-four rats were observed for the following conditions over a 32 day period.

    ______________________________________                                                       DESCRIPTION                                                      ______________________________________                                         Normal          Normal lens, no vacuoles                                       Time to begin   Vacuoles just beginning to                                     cataract formation                                                                             appear around lens perimeter                                   Time to vacoule Vacuolization clearly visible                                                  on anterior lens surface                                       Time to         Small opaque "flecks" grossly                                  snowflake       visible in addition to vacuoles                                Time to nuclear Nuclear cataract; interior                                     cataract        lens completely opaque                                         ______________________________________                                    

Observations were made at days 2, 3, 4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30 and 32.

All rat eyes in treatment L (2-fluoro) groups and M (2,7-difluoro) groups were asymptomatic at the end of 32 days. All rat eyes in the Sarges groups developed snowflake-like opacities without any indication of eariler vacuole formation. The average time to snowflake-like opacities was 15.7 days for the Sarges Racemic 4 Mg/Kg group and 19.7 days for the Sarges Racemic 8 Mg/Kg group. This difference is statistically (p<0.05) significant. Rat eyes in the galatose control group followed the usual pattern of cataract formations. The average time to snowflake was 11.5 days. This was statistically (p<0.05) significantly lower than the average for either Sarges group.

The "time to cataract" is summarized in Table V.

                  TABLE V                                                          ______________________________________                                         Times to Cataract                                                                                                 Standard                                    Treatment     Range (days)                                                                              Mean (day)                                                                               Deviation                                   ______________________________________                                         Sarges        12 to 22   15.68     2.68                                        Racemate 4 Mg/Kg/day                                                           Sarges        14 to 30   19.68     4.68                                        Racemate 8 Mg/Kg/day                                                           ______________________________________                                    

The "time to cataract" is on the average 4 days less for Sarges Racemic 4 Mg/Kg/day compound than for the Sarges Racemic 8 Mg/Kg/day compound. This difference is statistically significant at the 95% probability level.

Rat eyes in the galactose control group followed the usual pattern of cataract formation. The times to each type of cataract activity are summarized in Table VI.

                  TABLE VI                                                         ______________________________________                                         Times to Cataract for Galactose Control                                                                           Standard                                    Stage       Range (days)                                                                              Mean (day)  Deviation                                   ______________________________________                                         Time to early                                                                              3 to 4      3.58       0.50                                        vacoules                                                                       Time to vacoules                                                                           4 to 10     6.00       2.00                                        Time to snow-                                                                              8 to 18    11.50       2.30                                        flake                                                                          Time to nuclear                                                                            16 to 32   24.04       6.52                                        cataract                                                                       ______________________________________                                    

All but 3 rat eyes (12.5%) developed nuclear cataracts by Day 32. The time to nuclear is estimated as 35 days for these three rats in the computation of the mean and standard deviation.

At Day 32, three rats were selected and sacrificed at random from the groups treated with the racemic 2-fluoro derivative at 4 Mg/Kg/day, the racemic 2-fluoro derivative 8 Mg/Kg/day, 2,7-difluoro derivative 4 Mg/Kg/day, 2,7-difluoro derivative at 8 Mg/Kg/day and the Sarges Racemic compound at 4 and 8 Mg/Kg/day, and the dulcitol levels (galactitol and galatose) in the lenses were measured.

The average galactitol levels for Sarges Racemic at 4 Mg/Kg/day and Sarges Racemic derivative at 8 Mg/Kg/day were 9.238 and 9.107 respectively, and are statistically (p<0.05) significantly greater than the averages for the racemic 2-fluoro derivative at 4 Mg/Kg/day and the racemic 2-fluoro derivative at 8 Mg/Kg/day, 6.274 and 5.074 respectively, and the averages for 2,7-difluoro derivative at 4 and 8 Mg/Kg/day 2.560 and 1.399 respectively. The average galactitol levels for both doses of the 2,7-difluoro derivative are statistically (p<0.05) less than the average for either dose of the racemic 2-fluoro compound. Both the racemic 2-fluoro and the 2,7-difluoro derivatives inhibit cataract development. The 2,7-difluoro derivative is more potent than the 2-fluoro compound. A dose response relationship is observed between the 4 and the 8 mg racemic 2-fluoro compound.

B. In vivo dose response studies were conducted to test the in vivo activity of the following compounds by intubation (per oral) in galactocemic rats on a 30% galactose diet previously described:

L* dl-Spiro-[2-fluorofluoren-9,4'-imidazolidine]-2',5'-dione

M Spiro-[2,7-difluorofluoren-9,4'-imidazolidine]-2',5'-dione; and

Sarges dl-Spiro-[6-fluorochroman-4,4'-imidazolidine]-2,5'-dione.

Stock suspensions of the test compounds and all dilutions of the compound were formulated with 0.03% by weight Tween 80.

EXPERIMENTAL DESIGN

Healthy, Charles River CD (outbred albino, Sprague-Dawley derived) male rats, aged 20-30 days, without observable ocular defects and ranging in weight from 35-45 grams, were acclimated to experimental conditions (in quarantine) for two days prior to beginning the study.

Rats were individually assigned to one of twenty-three groups according to a random number schedule. Two rats, belonging to the same drug-diet treatment group, were housed per cage. Treatment and control groups consisted of six (6) rats each with no replacement in the event of death, and were designated as follows:

    ______________________________________                                                      No.                                                                            Rats     Drug      Doses/                                                                               No.                                      Group        (mg/kg)  Dose      Day   Days                                     ______________________________________                                         Sarges Racemic.sub.A                                                                        6        40.000    1     14                                       Sarges Racemic.sub.B                                                                        6        12.600    1     14                                       Sarges Racemic.sub.C                                                                        6        4.000     1     14                                       Sarges Racemic.sub.D                                                                        6        1.260     1     14                                       Sarges Racemic.sub.E                                                                        6        0.400     1     14                                       Sarges Racemic.sub.F                                                                        6        0.126     1     14                                       Sarges Racemic.sub.G                                                                        6        0.040     1     14                                       2-fluoro (L).sub.A *                                                                        6        40.000    1     14                                       2-fluoro (L).sub.B *                                                                        6        12.600    1     14                                       2-fluoro (L).sub.C *                                                                        6        4.000     1     14                                       2-fluoro (L).sub.D *                                                                        6        1.260     1     14                                       2-fluoro (L).sub.E *                                                                        6        0.400     1     14                                       2-fluoro (L).sub.F *                                                                        6        0.126     1     14                                       2-fluoro (L).sub.G *                                                                        6        0.040     1     14                                       Difluoro (M).sub.A                                                                          6        40.000    1     14                                       Difluoro (M).sub.B                                                                          6        12.600    1     14                                       Difluoro (M).sub.C                                                                          6        4.000     1     14                                       Difluoro (M).sub.D                                                                          6        1.260     1     14                                       Difluoro (M).sub.E                                                                          6        0.400     1     14                                       Difluoro (M).sub.F                                                                          6        0.126     1     14                                       Difluoro (M).sub.G                                                                          6        0.040     1     14                                       Positive     6        0.000     1     14                                       Galactocemic                                                                   Vehicle Control**                                                              Positive     6        0.000     0     14                                       Galactosemic                                                                   Control                                                                        ______________________________________                                          *Racemic                                                                       **This group was given an average dose of vehicle based on body weight.  

Lenses of all eyes were examined with a hand-held ophthalmoscope in the early stages of cataract development and a penlight for the stages, snowflake-like, snowflake, and nuclear cataract. Lens grading occurred every day for the first ten study days, and then every other day until study Day 14.

The test was to determine the relative efficacy and potency of the dl-2-fluoro and 2,7-difluoro compounds in terms of equal amounts of test drug per kg of body weight relative to Sarge's dl-spiro-[6-fluorochroman-4,4'-imidazolidine]-2',5'-dione, the positive anticataract control.

The relative potency determination was made at 7 drug levels over half log dose intervals. The response (percent cataracts formed and/or the time to cataract formation) was plotted against mg/kg and/or moles/kg.

ASSUMPTIONS ON EXPERIMENTAL DESIGN

The study was directed to the suppression and/or elimination of the initial stages of cataract development characterized by vacuoles or snowflake-like opacities only. It was assumed therefore that suppression and/or elimination of vacuoles or lens opacification by the test drugs affects the transport, absorption and/or metabolism of galactose in such a manner as to prevent subsequent osmotic disturbances normally leading to tissue degeneration and advanced cataract. Advanced cataract defined as stages 2-4 of the Sipple classification was assumed to be of secondary importance to the etiology of cataract inhibition.

In the event where cataract stage other than vacuole formed, such as snowflake-like opacities, this cataract was counted similarly as vacuole in percent cataract formation.

Studies demonstrate that 90% of young rats (50 gram) fed a 30% galactose diet will develop vacuole cataracts within 5-7 days. This study yielded this expected effect in the control groups.

EXPERIMENTAL PROCEDURES

All animals were fed Purina Laboratory Chow and water, ad libitum, for the two day acclimation period. All drugs were dosed orally by intubation using an animal feeding needle (Popper and Sons), 18 or 20 gauge, attached to a 1 or 3 ml syringe. Once the dosing time schedule was established, the schedule was followed throughout the study to compensate for any diurnal variation.

The animals were kept on a twelve hour day/night cycle. The temperature and humidity were determined each day at the scheduled dosing time of 1:00 p.m.

The animals were weighed every other day and adjustments to dosage amounts to compensate for weight gain were made each day prior to the dose time. All food was routinely withheld from all animal groups for four hours (9:00 a.m.) prior to the drug dose and restored two hours (3:00 p.m.) post-dose. Otherwise sufficient amounts of chow or diet mixture were maintained in the food hopper to allow the animals to eat ad libitum. There were two days of drug dosage with the animals remaining on Purina Laboratory Chow (Days 1 and 2). The 30% galactose diet mixture was introduced to the animals two hours post-dose on Day 3 which constituted Day 1 of the study.

OCULAR EXAMINATION AND GRADING

All eyes were examined with a hand-held ophthalmoscope and/or penlight at the times designated in the Experimental Design section.

It has been found in previous studies that dilation of the eye with a mydriactic (i.e. Mydriacyl) is not necessary for accurate grading, due to the semi-transparent nature of the rat iris. In the early stages (i.e., grades -, ±, and +) the lens was observed by reflecting the ophthalmoscope beam off the retina back through the lens and iris. Using this technique, vacuoles appear as dark, almost opaque patches. In the latter opacity stages (grades SL, S and N) the lens were observed grossly with a penlight. Each eye was given one of the following grades:

    ______________________________________                                         Grade   Description                                                            ______________________________________                                         -       Normal lens, no vacuoles                                               ±    Vacuoles just beginning around lens perimeter                          +       Vacuoles cover greater than 1/3 of lens                                        surface                                                                S       Lens completely opaque; small opaque "flecks"                                  visible in lens                                                        N       Nuclear cataract; white crystalline material                                   present in lens center                                                 SL      Small opaque "flecks" visible with no vacuoles                                 present (snowflake-like)                                               ______________________________________                                    

STATISTICAL ANALYSIS

The percent of eyes with vacuoles (cataracts) and/or the time to vacuole formation were analyzed for each treatment/concentration group. Since the data were sufficient, the potency of the 2,7-difluoro and racemic 2-fluoro compounds relative to the control were estimated by a probit analysis or other appropriate methodology.

Additionally, the incidence of non-formation (vacuoles, snowflake and nuclear cataract) were determined at selected time points during the study and used to compare drugs and concentration. This was done in an effort to identify an optimal endpoint for this type of study.

                                      TABLE VII                                    __________________________________________________________________________     Sarges Racemic* Versus Examples L                                              (Racemic 2-fluoro) and M (2,7-difluoro)                                                  Dose Day                                                             Drug      (mg/kg)                                                                             0 1 2 3 4 5 6 7 8  9  10 12 14                                  __________________________________________________________________________     Sarges Racemic                                                                           40   0 0 0 0 0 0 0 0 0  0  0  0  0%                                  2-fluoro**                                                                               40   0 0 0 0 0 0 0 0 0  0  0  0  0                                   2,7-difluoro                                                                             40   0 0 0 0 0 0 0 0 0  0  0  0  0                                   Sarges Racemic                                                                           12.6 0 0 0 0 0 0 0 0 0  0  0  0  8                                   2-fluoro**                                                                               12.6 0 0 0 0 0 0 0 0 0  0  0  0  0                                   2,7-difluoro                                                                             12.6 0 0 0 0 0 0 0 0 0  0  0  0  0                                   Sarges Racemic                                                                           4.0  0 0 0 0 0 0 0 0 0  0  0  17 50                                  2-fluoro**                                                                               4.0  0 0 0 0 0 0 0 0 0  0  0  0  0                                   2,7-difluoro                                                                             4.0  0 0 0 0 0 0 0 0 0  0  0  0  0                                   Sarges Racemic                                                                           1.26 0 0 0 0 0 0 0 0 8  17 83 100                                                                               100                                 2-fluoro**                                                                               1.26 0 0 0 0 0 0 0 0 0  0  0  0  0                                   2,7-difluoro                                                                             1.26 0 0 0 0 0 0 0 0 0  0  0  0  0                                   Sarges Racemic                                                                           0.4  0 0 0 0 0 0 33                                                                               33                                                                               50 58 83 83 100                                 2-fluoro**                                                                               0.4  0 0 0 0 0 0 0 8 42 42 67 83 100                                 2,7-difluoro                                                                             0.4  0 0 0 0 0 0 0 0 0  0  0  0  0                                   Sarges Racemic                                                                           0.126                                                                               0 0 0 0 0 0 33                                                                               33                                                                               50 58 83 83 100                                 2-fluoro**                                                                               0.126                                                                               0 0 0 0 0 0 33                                                                               33                                                                               50 50 50 83 83                                  2,7-difluoro                                                                             0.126                                                                               0 0 0 0 0 0 8 25                                                                               67 67 67 67 75                                  Galactose Control                                                                             0 0 0 0 0 0 33                                                                               50                                                                               100                                                                               100                                                                               100                                                                               100                                                                               100                                 Vehicle/Galactose                                                                             0 0 0 0 0 0 17                                                                               58                                                                               83 83 83 100                                                                               100                                 __________________________________________________________________________

The same data as in Table VII may be illustrated in a different format.

                                      TABLE VIII                                   __________________________________________________________________________     Percent of Rat Eyes (n = 12) With at Least Vacuoles Formed                     Day 6     Day 7                                                                              Day 8                                                                               Day 9                                                                               Day 10                                                                              Day 12                                                                             Day 14                                        __________________________________________________________________________     Sarges Racemic                                                                 40.000                                                                               0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         12.600                                                                               0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.3%                                         4.000 0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  16.7%                                                                              50.0%                                        1.260 0.0%                                                                               0.0%                                                                               8.3% 16.7%                                                                               83.3%                                                                               100.0%                                                                             100.0%                                        0.400 33.3%                                                                              33.3%                                                                              50.0%                                                                               58.3%                                                                               83.3%                                                                                83.3%                                                                             100.0%                                        0.126 33.3%                                                                              33.3%                                                                              41.7%                                                                               75.0%                                                                               100.0%                                                                              100.0%                                                                             100.0%                                        0.040 0.0%                                                                               8.3%                                                                               50.0%                                                                               66.7%                                                                               100.0%                                                                              100.0%                                                                             100.0%                                        Racemic 2-fluoro (L)                                                           40.000                                                                               0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         12.600                                                                               0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         4.000 0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         1.260 0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         0.400 0.0%                                                                               8.3%                                                                               41.7%                                                                               41.7%                                                                               66.7%                                                                                83.3%                                                                             100.0%                                        0.126 33.3%                                                                              33.3%                                                                              50.0%                                                                               50.0%                                                                               50.0%                                                                                83.3%                                                                              83.3%                                        0.040 33.3%                                                                              50.0%                                                                              83.3%                                                                               83.3%                                                                               100.0%                                                                              100.0%                                                                             100.0%                                        2,7-difluoro (M)                                                               40.000                                                                               0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         12.600                                                                               0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         4.000 0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         1.260 0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         0.400 0.0%                                                                               0.0%                                                                               0.0%  0.0%                                                                               0.0%  0.0%                                                                               0.0%                                         0.126 8.3%                                                                               25.0%                                                                              66.7%                                                                               66.7%                                                                               66.7%                                                                                66.7%                                                                              75.0%                                        0.040 50.0%                                                                              66.7%                                                                              83.3%                                                                               83.3%                                                                               91.7%                                                                               100.0%                                                                             100.0%                                        Vehicle                                                                              33.3%                                                                              50.0%                                                                              100.0%                                                                              100.0%                                                                              100.0%                                                                              100.0%                                                                             100.0%                                        Control                                                                        Untreated                                                                            16.7%                                                                              58.3%                                                                              83.3%                                                                               83.3%                                                                               83.3%                                                                               100.0%                                                                             100.0%                                        Control                                                                        __________________________________________________________________________     At observation day 12, the log relative potencies for eyes with vacuoles       or more                                                                        advanced cataracts with their 95% confidence limits are:                                         Log  (95% Confidence                                                           Potency                                                                             Limits)                                                 __________________________________________________________________________     2-fluoro*         0.6605                                                                              (0.3889 to 0.9346)                                      (L) relative to Sarges Racemic                                                 2,7-difluoro      1.1114                                                                              (0.8501 to 1.3852)                                      (M) relative to Sarges Racemic                                                 2,7-difluoro      0.4473                                                                              (0.1898 to 0.7144)                                      (M) relative to 2-fluoro*(L)                                                   __________________________________________________________________________     The antilogs of the relative potencies with their 95% confidence limits        are:                                                                                             Relative                                                                            (95% Confidence                                                           Potency                                                                             Limits)                                                 __________________________________________________________________________     2-fluoro*         4.58 (2.45 to 8.60)                                          (L) relative to Sarges Racemic                                                 2,7-difluoro      12.92                                                                               (7.08 to 24.28)                                         (M) relative to Sarges Racemic                                                 2,7-difluoro      2.80 (1.55 to 5.18)                                          (M) relative to 2-fluoro*(L)                                                   __________________________________________________________________________      *Racemic                                                                 

C. Polyol Accumulation in Diabetic Rat Lens and Sciactic Nerves

As a further test of the efficacy of the racemic 2-fluoro and 2,7-difluoro compound versus the Sarges Resolved compound, observation was made of the in vivo inhabition of polyol accumulation in the sciactic nerve and lens of rats with streptozotocin induced diabetic rats. The basis and techniques of the experiment are described in "Polyol Accumulation In Nervous Tissue Of Rats With Experimental Diabetes And Galactosaemia", M. A. Steward, W. R. Sherman, Mary M. Kurien, G. I. Moonsammy and M. Wisgerhof, Journal of Neuorchemistry, 14 (1967) 1057-1066.

In the test, eight male Sprague-Dawley rats weighing about 150 g were fasted overnight and given an injection of streptozotocin the next day. The dose was 9-10 mg/100 g of animal weight in an acid citrate buffer diluted in normal saline. The injection was given in or near the tail vein.

The respective aldose reductase inhibitors (the Sarges Resolved, racemic 2-fluoro, and 2,7-difluoro compounds) were given to 4 of the rats at 4, 8 and 24 hours. The dose of 0.15 mg/100 g animal weight was given orally in about 5 μl of water. Each inhibitor was mixed in an erude suspension of water with a mortar and pestle. An aliquot of this mixture was then taken, using an automatic pipet and fed to each animal.

On the day following the streptozotocin injection, the blood glucose of the animals was determined using the glucose oxidase-peroxidase method. At 27 hours all the animals were sacrificed and the lenses and sciatic nerves were removed, weighed and homogenized. These homogenates were then analyzed for sorbitol content using the GLC method. The experimental group (which was fed the inhibitor) was compared with the controls (not fed inhibitor) and the percentage of inhibition was determined. Each value represents comparison of 4 values for control and 4 for experimental. The results of the test are shown in Table IX.

                  TABLE IX                                                         ______________________________________                                         In vivo Inhibition of Polyol Accumulation in                                   the Sciactic Nerve and Lens of Streptozotocin Induced                          Diabetic Rats                                                                             mg/deciliter Average                                                                        Percent Inhibition                                     Compound     Blood Glucose* Nerve    Lens                                      ______________________________________                                         Sarges Resolved**                                                                           298 ± 17    77%      83%                                       Racemic 2-fluoro(L)                                                                         425 ± 39    96%      92%                                       2,7-difluoro (M)                                                                            349 ± 32    90-95%   95%                                       ______________________________________                                          *Eight animals were used for each study, 4 control, 4 experimental.            **dSpiro-[6fluorochroman-4,4imidazolidine2',5dione                       

D. Nerve Conduction Study In Diabetic Rats

The purpose is to evaluate the efficacy of the racemic 2-fluoro compound (L), an aldose reductase inhibitor, for inhibiting cataractogenesis and nerve conduction deficit in diabetic rats.

METHODS AND MATERIALS

Diabetes was induced in male albino rats by the intravenous injection of 50 mg/kg streptozotocin. The diabetic state was verified by measuring the blood glucose level in each animal before and after injection. Diabetic animals were assigned randomly to three groups as follows: (1) vehicle treated control; (2) 8 mg/kg the racemic 2-fluoro compound (L); and (3) 16 mg/kg Sarges Racemic. A fourth group consisted of non-diabetic and otherwise normal rats which remained untreated. Treatments were given once daily by oral lavage, and continued through the day prior to sacrifice of the animal.

Each animal was weighed on a weekly basis. Both lenses of each animal were examined by ophthalmoscope periodically and any cataractous changes were graded and noted. At the end of 15 weeks, each animal was anesthetized using pentobarbital and the nerve conduction velocities of the sciatic nerve were measured. After an animal was sacrificed, the sciatic nerve and other tissues and organs were taken, weighed, and frozen for future biochemical analyses.

RESULTS

Cataractous changes were graded on a scale of 0 to 4; 0 denoting a normal looking lens with no changes and 4 denoting opacification involving the whole lens. The lenses of those rats in the untreated, normal control group exhibited no apparent changes and remained optically clear. Of the 32 lenses (16 rats) present at the end of 15 weeks in the vehicle-treated diabetic rats, 27 had a score of 4, 3 scored 3, and 2 scored 2 on cataractous changes. Thus, every lens exhibited maximal or near maximal opacity. Racemic 2-fluoro compound (L) was effective in preventing opacification of the lens in diabetic rats. Of 30 lenses (15 rats) in the Sarges Racemic-treated group, all appeared normal. Thus, both compounds were effective for preventing cataracts in diabetic rats at 8 mg/kg of the racemic 2-fluoro compound and 16 mg/kg of the Sarges Racemic compound.

The record of electrical activity from the sciatic nerve in response to electrical stimulation of the nerve exhibited two inflections and two peaks, probably representing different nerve fiber groups. The effect of treatment on each of the four events was determined, and all are considered, although treatment effects appear to be greatest on the first inflection. By comparison to the normal, untreated controls, the conduction velocities determined for the vehicle-treated, diabetic rats were as follows: first inflection, 83% of normal; first peak, 82% of normal; second inflection, 80.6% of normal; and, second peak, 76.4% of normal. Thus, the impairment of nerve conduction, as manifest by a reduction in velocity of conduction, ranged from 17% to 23.6% and its attributable to the diabetic state of these animals. In those rats (diabetic) treated with the racemic 2-fluoro compound (L), the nerve conduction velocities as a percent of normal were as follows: first inflection, 93.3%; first peak, 88.2%; second inflection, 87.4%; and second peak, 85.0%. In these animals, then, the impairment ranged from 6.7% to 15%, representing an improvement by treatment of 34% to 61%. In those diabetic rats treated with Sarges Racemic, the nerve conduction velocities as a percent of normal were as follows: first inflection, 88.6%; first peak, 83.9%; second inflection, 82.4%; second peak, 79.1%. This represents an impairment ranging from 11.4% to 20.9%, indicating an improvement over controls of 9% to 33%. Therefore, both the racemic 2-fluoro compound (L) and Sarges Racemic produce some beneficial effect to improve nerve conduction velocity and return it towards normal. However, the racemic 2-fluoro compound (L), at one-half the dose of Sarges Racemic, allows a greater improvement. Statistical analysis indicates that only the improvement by the racemic 2-fluoro compound (L) is significant, by comparison to the untreated diabetic rats.

It should be understood that while certain preferred embodiments of the present invention have been illustrated and described, various modifications thereof will become apparent to those skilled in the art. Accordingly, the scope of the present invention should be defined by the appended Claims and equivalents thereof.

Various features are set forth in the following claims. 

I claim:
 1. A method for treating diabetic complications in mammals comprising administering an effective amount of spiro-(fluoren-9,4'-imidazolidine)-2',5'-dione or pharmaceutically acceptable salt thereof having the formula ##STR27## where x,y, and z are selected from the group consisting of NH₂, NO₂, and CO₂ H.
 2. A method for treating diabetic complications in mammals comprising administering an effective amount of spiro-(fluoren-9',4'-imidazolidine)-2',5'-dione or pharmaceutically acceptable salt thereof having the formula ##STR28## 